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Re: [patch] Improve loop array prefetch for IA-64


On 6/2/06, Canqun Yang <canqun@yahoo.com.cn> wrote:
This patch results a performance increase of 4% for SPECfp2000 and 13% for NAS benchmark suite on
Itanium-2 system, respectively. More performance increase is hopeful by further tuning the
parameters and improving the prefetch algorithm at tree level.

Bravo.


--- ia64.h (revision 114307)
+++ ia64.h (working copy)
@@ -1985,13 +1985,18 @@
   ??? This number is bogus and needs to be replaced before the value is
   actually used in optimizations.  */

-#define SIMULTANEOUS_PREFETCHES 6
+#define SIMULTANEOUS_PREFETCHES 18

Is the number still bogus as the comment suggests, or is there a rationale for 18? It looks quite high.

+/* A number that should roughly corresponding to the nunmber of instructions
+   executed before the prefetch is completed.  */
+
+#define PREFETCH_LATENCY 400

Likewise. Is 400 cycles the memory latency on itanium-2?


Gr.
Steven


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